(274b) Modular CO2 Capture from Distributed Oilfield Engines

There are over 4,000 gas-fired rich-burn reciprocating engines (1 MW scale or higher) operating in North America, emitting an estimated 19 MMmt of CO2 per year. The majority of these engines are servicing oilfield operations and are in proximity to potential CO2 utilization opportunities. The following system design separates and captures CO2 from the exhaust gas of an engine that would otherwise be discharged to the atmosphere. Off-the-shelf components are combined in a modular design to provide a low-cost solution for capturing CO2 from small distributed sources.

This system utilizes the attractive characteristics of rich burn engine exhaust (high temperature, high CO2 concentration, low oxygen concentration) and automotive turbochargers to convert thermal energy to compression power to drive a membrane separation process.

The hot exhaust gas is routed through the shell side of a gas-gas heat exchanger where it transfers heat to a nitrogen-rich retentate stream. The exhaust is further cooled to condense and remove water and compressed from atmospheric pressure to 100-150 psia using two automotive turbochargers in series. The compressed exhaust is sent to a CO2-selective glassy polymer membrane which produces a permeate stream of 50-60% CO2 and a retentate stream of 5% CO2. The retentate stream, which is at 90-140 psia, is heated in the tube side of the gas-gas heat exchanger and then expanded in the automotive turbochargers to directly drive the compression process. The permeate stream is further concentrated using a mixture of membranes and heat-integrated refrigeration processes to either a 95% gaseous CO2 stream or a 99% liquid CO2 stream. Using turbochargers for the heat-recovery compression process significantly reduces the parasitic load demanded by an equivalent membrane process with traditional compression.

The design has been modeled in an Aspen HYSYS simulation with integrated algorithms for turbocharger and membrane performance estimations. The simulation produces performance results for various operational and ambient conditions to determine an estimation of the overall footprint, energy usage, and capital expenditure. System parameters are altered to optimize overall breakeven CO2 price.

Experimental results from a 1 MW scale turbocharger component test unit are used to validate the simulation and demonstrate the thermal energy in the rich burn engine exhaust is sufficient to drive the turbochargers. The optimized system estimates CO2 capture rate, capital expenditure, and energy consumption to produce a CO2 stream at a competitive price compared to other technologies.